Natural Resources
Conservation Service
Shallow to Loamy, Calcareous 15-19 Inch Precipitation Zone Lost River Mountains
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Transition T1B More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A More details
- Transition T3A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The reference state consists of three dominant plant communities: The black sagebrush (Artemisia nova) dominated community, the the mixed early sagebrush (Artemisia arbuscula ssp. Longiloba) and black sagebrush dominated community, and a community where overstory shrub canopy dominance is usurped by bunchgrasses. The greatest difference between the three plant communities is composition and foliar cover of sagebrush (Artemisia) species, and may include mountain big sagebrush (Artemisia tridentata ssp. Vasayana). Mountain big sagebrush foliar cover increases on sites that are closer to the high end of the effective precipitation range (15 to 19 inches) and the calcium carbonate equivalency in the soil is lower, closer to minimum 15 percent concentrations outlined in the site concept.
Processes (both natural and anthropogenic) that result in state and community changes include fire, grazing, land use change, and occurrence of invasive species (Davies et al., 2011).
Characteristics and indicators
The shift between plant communities at this ecological site is generally driven by calcium carbonate concentration in soils, effective precipitation, and sagebrush killing disturbances or lack thereof. Historically, low to mixed severity fires occurred at relatively frequent fire return intervals of 10 to 25 years, limiting sagebrush canopy density and creating a mosaic of sagebrush stands and more open grasslands (Knick, Holmes, & Miller, 2005). Exclusion of fire (in conjunction with climate change) increases sagebrush canopy cover and can lead to more severe stand replacing fires, often times at more frequent intervals. These severe fires can drive shifts to grassland communities as well as create opportunities for invasive species establishment (Roadhouse, Irvine, & Bowerstock, 2020; Knick et al., 2005).
Improper grazing practices can also lead to an increase in sagebrush canopy cover and increased risk of severe, stand replacing fire occurrence. Removal of understory grasses can lessen the opportunities for low severity fires which leads to increased canopy densities and increases potential for severe fire disturbance events (Knick et al., 2005).
Resilience management
This site has moderate to high resilience as a result of the cryic soil temperature regime and xeric soil moisture regime. Resistance and resilience of a specific site has been attributed with abiotic conditions favorable to plant growth and reproduction (Maestas et al. 2016). Soils that fall within the cryic (cold) temperature regime and xeric (wet) moisture regime tend to have higher diversity and production, and are therefore more resilient, specifically in terms of resisting or recovering from invasion post disturbance (Maestas et al., 2016).
On the LRU scale, this site may also have increased resistance to invasion of annual grasses due to the calcium carbonate concentration found in the 10 to 25 centimeter range of the soil profile. Calcareous soils have shown to provide a deterrent to establishment of invasive grasses such as Bromus tectorum (Miller et al., 2006).
Dominant plant species
black sagebrush (Artemisia nova), shrub
little sagebrush (Artemisia arbuscula ssp. longiloba), shrub
mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub
bluebunch wheatgrass (Pseudoroegneria spicata), grass
spiny phlox (Phlox hoodii), grass
Submodel
Description
When a Shallow to Loamy, Calcareous ecological site enters the Grazing Resistant state, the primary shift occurs in the understory vegetation. Grazing pressure from livestock, native ungulates, or a combination of the two drives a shift from the cool-season bunch grasses present in the Reference State towards rhizomatous wheatgrasses, short-stature bunch grasses, and ground covering forbs. This state is generally a result of current or historic improper grazing practices that potentially included higher socking rates and repeated heavy grazing during the growing season.
Characteristics and indicators
In this state, total canopy cover and production values for mid to large sized bunchgrasses such as bluebunch wheatgrass will decrease. These understory grasses will be relegated to the protected areas under the sagebrush canopies where they are sheltered from grazing. As they are removed from the canopy gaps, they will be replaced with grazing resistant short-stature bunch grasses like Sandberg bluegrass (Poa secunda) and rhizomatous wheatgrasses such as thick spike wheatgrass (Elymus lanceolatus), Western wheatgrass (Pascopyrum smithii), and at the higher end of the precipitation range, slender wheatgrass (Elymus trachycaulus). Openings in the canopy gaps vacated by bunchgrasses also present opportunities for an increase in disturbance tolerant forbs such as Hood's phlox (Phlox hoodii), cushion phlox (Phlox pulvinata), vetch species (Vetch sp.) and Indian paintbrush species (Castilleja sp.). Opportunities for invasive annual grasses also increase as competition from native grasses is removed from the canopy gaps.
Depending on how well grazing resistant rhizomatous and bunchgrasses occupy the canopy gaps, an increase in bare ground cover usually occurs. This can lead to increased erosion and decreased infiltration, decreasing available moisture. Because of this, productivity and canopy cover will be lower than at the Reference State.
Resilience management
Resilience in this state is lower than in the Reference State, primarily due to the decrease in available moisture and the opportunity for invasive species recruitment. Ability to recover from disturbance in rangeland systems has shown to be related to local climatic conditions. As available moisture increases and temperature decreases, resilience to disturbance increases (Chambers, et al. 1014). At this ecological site, resilience of the black and little sagebrush dominated sites would tend to be lower than at the sites with mountain big sagebrush in the overstory canopy as this would indicate higher available moisture and lower average annual temperature.
Resilience to erosion and invasive species establishment would be dependent on how well rhizomatous grasses and forbs occupy the bare ground spaces left by the removal of bunchgrasses. Rhizomatous grasses are mat forming and if able to establish relatively quickly can aid in reducing erosion. Additionally, if native rhizomatous grasses and forbs are able to quickly establish, this decreases the ability of invasive annual grasses such as cheatgrass to occupy bare soil openings within the site.
Dominant plant species
black sagebrush (Artemisia nova), shrub
little sagebrush (Artemisia arbuscula ssp. longiloba), shrub
mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub
Sandberg bluegrass (Poa secunda), grass
spiny phlox (Phlox hoodii), grass
cushion phlox (Phlox pulvinata), grass
milkvetch (Astragalus), grass
Submodel
Description
The Disturbed state is a result of both natural and anthropogenic disturbance events that result in widespread sagebrush mortality. The primary natural disturbance resulting in sagebrush mortality at this ecological site is frequent or severe wildfire. Flooding, intense freeze events, and insect and disease can also occur. Because this LRU exists primarily on publicly managed lands (US Forest Service, Bureau of Land Management, and State), widespread anthropogenic disturbance events are infrequent. Examples of anthropogenic disturbance events include brush management through sagebrush mowing or removal treatments, chemical treatments, or improper grazing techniques that result in high intensity hoof disturbance.
A combination of natural and anthropogenic disturbance is possible and can result in increased severity of disturbance, decreased resilience, and greater difficulty returning to the Reference State. For example, improper grazing practices that result in chronic defoliation following a fire disturbance event can increase bare ground cover, increase erosion potential, and slow the reestablishment of grass species that preclude the return of overstory sagebrush canopy (Zlatnik, 1999).
Characteristics and indicators
The primary indicator of the Disturbed State is near to complete loss of overstory sagebrush species (black sagebrush, little sagebrush, and mountain big sagebrush). A shift towards an increase in native and non-native disturbance tolerant grasses and forbs is likely with removal of resource competition associated with sagebrush overstory. Additionally, canopy cover of disturbance tolerant shrubs such as yellow rabbitbrush (Chrysothamnus viscidiflorus) and rubber rabbitbrush (Ericameria nauseosa) may increase. Severe disturbance events also increase the opportunity for invasion of annual grasses and weeds such as cheatgrass (Bromus tectorum) and thistle species. Percent canopy cover of invasive species is dependent on distance of a seed source post disturbance. Initial cover of invasive species stays below 5 percent (Zlatnik, 1999).
Resilience management
Resilience in this state is moderate. Many of the post-disturbance grasses and shrubs that are common in this state establish quickly and reach a representative canopy within 10 years post-disturbance, and continue to increase until overstory canopy of sagebrush begins to return. However, local resilience in this state is highly dependent on current soil moisture availability, seed sources, timing and severity of the disturbance. In the instance of fire disturbance, bluebunch wheatgrass mortality can be significantly lower if the fire occurs in the spring as opposed to fall, and recovery can be impacted by quantity of immediate post-fire precipitation (Zlatnik, 1999).
More severe disturbances increase possibility of post-disturbance invasion. The greater the establishment of invasives, the lower the site resilience becomes.
Dominant plant species
yellow rabbitbrush (Chrysothamnus viscidiflorus), shrub
mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub
bluebunch wheatgrass (Pseudoroegneria spicata), grass
Sandberg bluegrass (Poa secunda), grass
stemless mock goldenweed (Stenotus acaulis), grass
Indian paintbrush (Castilleja), grass
Submodel
Mechanism
Transition from the Reference state to the Grazing Resistant state is a product of current or historical improper grazing practices that resulted in chronic defoliation of vegetation. Continual overstocking and overgrazing during critical growing periods can result in a significant functional and compositional shift in the understory vegetation of the Shallow to Loamy Calcareous ecological site. In perennial bunchgrasses such as bluebunch wheatgrass which is the dominant understory vegetation in the Reference State, repeated overgrazing weakens the underground structures through undernourishment caused by the continual removal of photosynthetic tissue (Daubenmire, 1940). This eventually results in death of these grasses, opening the canopy for grazing resistant grasses like Sandberg bluegrass, or bare soil. Because most of this LRU exists on publicly managed lands with regulated grazing policies, new transitions to this state are rare. Historical practices and regulations may have differed, leading to current existence of this state.
Constraints to recovery
Constraints to recovery include: o Continued improper grazing techniques o Prolonged periods of drought that diminish regeneration of desired species o Loss of nutrient rich top soil due to increased erosion o Establishment of invasive species
Context dependence
Restoration efforts can be greatly influenced by precipitation patterns. Successful regeneration of Reference State understory species is highly dependent on moisture received post restoration efforts. Rates of successful establishment of bluebunch wheatgrass and Sandberg bluegrass increase when available moisture is high during critical regeneration periods (Zlatnik, 1999 & Howard, 1997).
Mechanism
Transition from the Reference to the Disturbed State is primarily a mechanism of severe disturbance, both natural and anthropogenic. In this this ecological site, the most likely disturbance to cause this transition is frequent or severe wildfire events. Other disturbances include but are not limited to flooding, freeze kill, insect and disease, and mechanical brush removal.
Constraints to recovery
Primary constraint to recovery is distance to seed source. When the disturbance is severe enough and the extent is great, seed source populations for sagebrush species may be removed from the vicinity. In this case, immigration and re-establishment of overstory sagebrush species can be slow. This time period can be greatly reduced through seeding and planting interventions.
Context dependence
The primary factor driving likelihood of restoration success is post disturbance weather patterns. Prolonged period of drought can slow restoration processes, whereas average to above average precipitation post disturbance can greatly increase speed and success in re-establishment of sagebrush species (Robin, 2017; Steinberg, 2002; and Fryer, 2009).
Mechanism
The primary mechanism of restoration back to the Reference State is time without grazing. Seeding of desired Reference State species can speed up the restoration process.
Context dependence
Time frame for restoration is highly dependent on variations in localized weather patterns. Prolonged periods of drought can dramatically increase time required to return to the Reference State, whereas periods of above normal precipitation can decrease that time frame. Grazing practices that are infrequent and of light intensity, mimicking natural historic grazing patterns will not impact the restoration pathway. However, continuous early season grazing at moderate to high intensity resulting in significant defoliation will perpetuate the Grazing Resistant State.
Mechanism
Transition from the Grazing Resistant to the Disturbed State is a result of moderate to severe sagebrush removing disturbances. These can include both natural and anthropogenic disturbances; however, unlike the Reference State, possibility of moderate to severe fire events is reduced as a result of the diminished understory present in the Grazing Resistant State.
Mechanism
The most important mechanism driving restoration from the Disturbed to the Reference State is time without sagebrush removing disturbances and distance from overstory species (sagebrush) seed source. Seeding or planting of desired overstory species in the Reference State can accelerate restoration efforts.
Context dependence
Restoration is highly dependent on time without disturbance. New sagebrush seedlings that are able to establish on a site are moderately sensitive to disturbances such as flood, freeze, and insect and disease. They are highly sensitive to herbivory and even low severity fire occurrence (Fryer, 2009 & Steinberg 2002). Seeding and planting of desired species can speed up the restoration process, however, regeneration success with or without planting is highly dependent on localized weather patterns during this restoration period. Periods of drought will slow the process significantly, whereas periods of above normal precipitation aid in sagebrush regeneration and establishment (Innes, 2017; Steinberg 2002 & Fryer, 2009).
Mechanism
Transition from the Disturbed to the Grazing Resistant State results from improper grazing practices that result in chronic defoliation. Plant communities in the Disturbed State are particularly vulnerable to heavy grazing in the years immediately following the disturbance that initiated the transition. If bunchgrasses are unable to establish, plant composition could shift to more grazing resistant, rhizomatous grass species.
Context dependence
Years of drought or below average precipitation in combination with improper grazing that results in chronic defoliation can accelerate transition to the Grazing Resistant State.
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